(a) Field of the Invention
The present invention relates to a stabilized isothiazolone composition and a method of stabilization of isothiazolone, more particularly, to a stabilized isothiazolone solution comprising (a) an isothiazolone compound of formula I, (b) sulfuric acid, and (c) solvent. 
where
R1 and R2 each independently represent a hydrogen atom, a halogen atom, or C1-C4 alkyl group, or R1 and R2 together form a cyclic allyl group;
R3 represents a hydrogen atom; C1-C10 alkyl group which is substituted or unsubstituted with a halogen atom or hydroxy group, C2-C10 alkenyl group which is substituted or unsubstituted with a halogen atom, C2-C10 alkynyl group which is substituted or unsubstituted with a halogen atom, C1-C10 alkyl group, or aralkyl group which is substituted or unsubstituted with C2-C9 alkoxy group.
The present invention also relates to a method of stabilization of isothiazolone of the formula I.
(b) Description of the Related Art
Since development by Craw et al. in 1965, isothiazolone compounds have been extensively used in many industrial fields as a disinfectant including an antibacterial and antimicrobial agent for dyes, cosmetics, fibers, or plastics, etc.
However, since isothiazolone is very unstable and easily degraded by moisture in the air, heat and ultraviolet light, the beneficial properties of the compound may be lost during storage. In order to improve the stability of isothiazolone, several methods have been actively developed, and the typical method is to use a metal salt stabilizer.
In U.S. Pat. Nos. 3,870,795 and 4,067,878, for example, metal nitrite or metal nitrate are added to stabilize isothiazolone solutions. But such metal salt stabilizers react with emulsion components in a latex emulsion to produce precipitates. Further, in some cases, chlorine ions in the metal salt may induce corrosion of the system and metal ions may increase the hardness of water to induce scale. Thus, in such cases, the use of the metal salt is undesirable.
A preferred disinfectant should be stable during use, but should be quickly degraded after use so as not to cause a persistent environmental problem. Accordingly, there is a need for a stabilizer satisfying these requirements.
A stabilized isothiazolone solution is provided that is useful as a disinfectant and antimicrobial agent, has high stability and can contain active ingredient in high concentration.
A method of stabilization of isothiazolone is also provided which can stabilize an isothiazolone longer than the conventional method using ferric salt, substantially prevents the formation of nitrosamine and precipitates, substantially prevents heavy metals from being discharged to the environment, substantially prevents ions such as Mg2+ from binding to ions contained in the industrial water such as PO43xe2x88x92, CO32xe2x88x92 to form a Hard Scale and does not use stabilizers comprising ferric salts.
The present invention provides a stabilized isothiazolone composition comprising (a) an isothiazolone of formula I, (b) sulfuric acid, and (c) solvent. 
where
R1 and R2 each independently represent a hydrogen atom, a halogen atom, or a C1-C4 alkyl group, or R1 and R2 together form a cyclic allyl group;
R3 represents a hydrogen atom, C1-C10 alkyl group which is substituted or unsubstituted with a halogen atom or hydroxy group, C2-C10 alkenyl group which is substituted or unsubstituted with a halogen atom, C2-C10 alkynyl group which is substituted or unsubstituted with a halogen atom, C1-C10 alkyl group, or aralkyl group which is substituted or unsubstituted with C2-C9 alkoxy group.
The present invention also provides a method of stabilization of isothiazolone comprising stabilizing isothiazolone by blending an isothiazolone and a stabilizer, where the isothiazolone is that of formula I, and the stabilizer is sulfuric acid.
The present invention also provides a method of sterilization of bacteria and/or fungi and/or algae or suppression of the growth thereof comprising applying disinfectant compositions in the area that is contaminated or contamination-vulnerable by bacteria and/or fungi and/or algae, wherein said disinfectant compositions are the stabilized isothiazolone solutions comprising (a) isothiazolone compound represented by the formula I, (b) sulfuric acid and (c) solvent.
Upon having endeavored to solve the problem of the conventional method of stabilization of isothiazolone, the present invention utilizes sulfuric acid as a stabilizer. Thus, the degradation of isothiazolone can be inhibited, and even completely prevented according to the present invention.
The stabilized isothiazolone solution of the present invention includes an isothiazolone compound represented by formula I, sulfuric acid and solvent.
The isothiazolone compound which may be used in the present invention illustratively includes one or more compounds selected from the group represented by formula 1, preferably one or more compounds such as 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 4,5-dichloro-2-methyl-4-isothiazolin-3-one, 5-chloro-2-n-octyl-4-isothiazolin-3-one, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one and benzoisothiazolin-3-one. It is more preferable to use 5-chloro-2-methyl-4-isothiazolin-3-one or 4,5-dichloro-2-methyl-4-isothiazolin-3-one alone or a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one. When using a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, the weight ratio is preferably about 50:50-99:1, more preferably about 60:40-95:5. In addition, it is also preferable to use a mixture comprising 2-methyl-4-isothiazolin-3-one as an active ingredient and a small amount of 5-chloro-2-methyl-4-isothiazolin-3-one. In such case, the weight ratio is preferably about 99.5:0.5-90:10, more preferably about 98:2-96:4.
The sulfuric acid used as stabilizer in the stabilized isothiazolone solution of the present invention preferably is high purity, such as spectroscopic or reagent grades.
The solvent contained in the stabilized isothiazolone solution can be any type of solvent which can effectively disperse the isothiazolone compound and sulfuric acid. Preferably the solvent is water. The amount of solvent can be varied according to the use of the stabilized isothiazolone solution. And, if the purpose is only storage, the solvent may not be used.
The stabilized isothiazolone solution according to the present invention may be made in the form of concentrated solution or diluted solution according to the purpose. When stabilized isothiazolone is employed in exceptional cases such as mass shipments, more concentrated solutions may be used. The isothiazolone solution comprises about 0.00001-99 wt % of one or more compounds selected from isothiazolone represented by formula I, 0.00001-99 wt % of stabilizer, and less than 99.99998 wt % of solvent. Preferably, it comprises 0.1-40 wt % of one or more compounds selected from isothiazolone represented by formula I, 0.1-99 wt % of stabilizer, and 99.8 wt % or less of solvent. Most preferably, it comprises 1-30 wt % of one or more compounds selected from isothiazolone represented by formula I, 5-99 wt % of stabilizer, and 94 wt % or less of solvent. Conventional isothiazolone solution using metal salt stabilizer can contain at most 14 wt % of active ingredient isothiazolone, while the stabilized isothiazolone solution of the present invention can contain up to 40 wt % of isothiazolone.
The amount of stabilizer may vary according to the conditions of use and the concentration of isothiazolone in a mixture; preferably, the weight ratio of isothiazolone:stabilizer is in the range of 1:0.01-1:1,000. This range is preferable in terms of stability and cost-saving. In the case of a concentrated solution, the weight ratio of isothiazolone:stabilizer is preferably in the range of 1:0.02-1:50. Even though more amount of stabilizer may be used, this is uneconomical. In the case of an extremely diluted isothiazolone solution having about 1-10,000 ppm of isothiazolone in solvent, the weight ratio of isothiazolone:stabilizer is preferably in the range of 1:0.1-1:20, more preferably in the range of 1:0.1-1:10.
As aforementioned, the stabilized isothiazolone solution according to the present invention is very stable in the air, its efficacy may be sustained under a relatively prolonged period of time in storage, and it forms smaller precipitates than the conventional isothiazolone solution using metal salt stabilizer. Further, the stabilized isothiazolone solution according to the present invention exhibits excellent antimicrobial and biocidal activities when the effective amount of the solution is applied to the area that is contaminated or contamination-vulnerable by microbes, and removes the hard scale forming factor. In particular, it has the merit that it is dissolved quickly and does not cause an environmental problem when discharged.
In other words, the stabilized isothiazolone solution may be extensively used in the following fields: germicidal agents, sanitary aids, purifier, deodorizer, soap in the form of liquid or powder, anti-oil and anti-greasing agents, chemical products for the treatment of foods, daily chemical products, food protectives, protectives for animal feeds, wood protectives, dyes, lazures, flavoring agents, medical preservatives including hospital, metal agents, dyeing solutions, cooling water, air purifier, petroleum manufacture, paper-treatment, anti-slime agent at a paper mill, petroleum products, adhesives, fibers, paint slurry, latex, treatment for leather articles, petroleum fuels, laundry disinfectants, blending feeds for farming, ink, mining, non-woven fabric, petroleum reservoirs, paste material, rubber, sugar refining, tobacco, swimming pool, cosmetics, commodities for toilet, pastes, plastics, cardboard, pharmaceuticals, chemical toilet paper, household laundries, additives for diesel fuel, wax, cork, lubricants, commodities for construction, blending or polishing agents for concrete; it may also be used in the area that is contaminated or contamination-vulnerable by bacteria, fungi or algae and in the places containing organic materials and water where undesirable microorganisms may grow.
The present invention is explained in more detail by the following illustrative examples. It is not intended that the scope of the claims be limited to these examples.
Isothiazolone solutions obtained from the following examples and comparative example were respectively left in an isothermal bath at 65xc2x0 C. to measure thermal stabilities. The degree of degradation was measured by high performance liquid chromatography (HPLC). The thermal stability was measured at 65xc2x0 C. In general, the thermal stability measured at 65xc2x0 C. during one week corresponds to that measured at 25xc2x0 C. during 7 months.